REG104FA-2.7SLASH500 datasheet(8/22 Pages) TI

8 / 22 page

SBVS025G

REG104

BASIC OPERATION

The REG104 series is a family of LDO (Low DropOut) linear

regulators. The family includes five fixed output versions

(2.5V to 5.0V) and an adjustable output version. An internal

DMOS power device provides low dropout regulation with

near constant ground pin current (largely independent of load

and dropout conditions) and very fast line and load transient

response. All versions include internal current limit and

thermal shutdown circuitry.

Figure 1 shows the basic circuit connections for the fixed

voltage models. Figure 2 gives the connections for the

adjustable output version (REG104A) and example resistor

values for some commonly used output voltages. Values for

other voltages can be calculated from the equation shown in

Figure 2.

FIGURE 1. Fixed Voltage Nominal Circuit for REG104.

REG104

Enable

OUT

0.1

µF

0.01

µF

Gnd

Out

Optional

FIGURE 2. Adjustable Voltage Circuit for REG104A.

OUT = (1 + R1/R2) • 1.295V

Pin numbers for SOT-223 package.

REG104

0.1

µF

Gnd

OUT

0.01

µF

OUT

Adj

ADJ

Load

Enable

To reduce current through divider, increase resistor

values (see table at right).

As the impedance of the resistor divider increases,

ADJ (~200nA) may introduce an error.

FB improves noise and transient response.

OUT (V)

1 (Ω)

(1)

2 (Ω)

(1)

1.295

Short

Open

2.5

12.1k

13k

1.21k

1.3k

16.9k

13k

1.69k

1.3k

3.3

20k

13k

2.0k

1.3k

37.4k

13k

3.74k

1.3k

NOTE: (1) Resistors are standard 1% values.

EXAMPLE RESISTOR VALUES

Optional

Enable

Z = 10V

175k

Ω

FIGURE 3. Enable Pin Equivalent Input Circuit.

None of the versions require an output capacitor for regulator

stability. The REG104 will accept any output capacitor type

less than 1

µF. For capacitance values larger than 1µF the

effective ESR should be greater than 0.1

Ω. This minimum

ESR value includes parasitics such as printed circuit board

traces, solder joints, and sockets. A minimum 0.1

µF low ESR

capacitor connected to the input supply voltage is recom-

mended.

ENABLE

The Enable pin allows the regulator to be turned on and off.

This pin is active HIGH and compatible with standard TTL-

CMOS levels. Inputs below 0.5V (max) turn the regulator off

and all circuitry is disabled. Under this condition ground-pin

current drops to approximately 0.5

µA.

When not used, the Enable pin may be connected to VIN.

Internal to the part, the Enable pin is connected to an input

resistor-zener diode circuit, as shown in Figure 3, creating a

nonlinear input impedance.

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